Method for forming cooling slot in airfoil blades

ABSTRACT

A cooling slot for passing cooling fluid through a heated plate such as an airfoil blade for use in gas turbine engines is created by forming a first plurality of passages within the blade, and then forming a second plurality of passages within the blade, wherein preselected of the passages of the second plurality intersect at least one of the passages of the first plurality to define a number of nodes between the points of intersection. When cooling fluid is passed through the blade, the nodes act as turbulence promoters and area increasers for improving convective heat transfer between the blade and the cooling fluid. 
     This is a divisional application of application Ser. No. 219,005 now U.S. Pat. No. 3,819,295 issued June 25, 1974 filed Sept. 21, 1972 and assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION

The present invention relates to the cooling of heated plates, and moreparticularly to the cooling thereof by means of a cooling slot passingtherethrough.

The invention herein described was made in the course of or under acontract, or a subcontract thereunder, with the United States Departmentof the Air Force.

The cooling of heated plates in various machinery types has beenperformed by a multiplicity of methods. One such method is the passingof a cooling fluid through a cooling slot within the plate. It has beenfound that the convective heat transfer of this type cooling is improvedin efficiency by promoting turbulence within the cooling slots.

Heated plate cooling concepts have found particular application in thegas turbine engine art wherein it is often desired to partially coolairfoil blades (of the compressor or turbine blade variety) by passingcooling fluid from an internal cavity within the blade through a coolingslot located in the trailing edge of the airfoil blade. In the past, thetrailing edge slot has been provided with a number of protuberances ornodes which extend from the walls of the slot into the slot and engagethe cooling fluid passing therethrough. These nodes serve the dualfunction of promoting turbulent fluid flow through the slot andadditionally of increasing the surface area of the trailing edgepresented to the cooling fluid. These two functions combine tosubstantially improve the efficiency of heat transfer from the trailingedge of the cooling fluid.

The fabrication of airfoil blades incorporating such a noded trailingedge slot has been a particular problem in the prior art, which hasrelied upon either casting or sheet metal fabrication techniques.Casting has limitations due to the relatively difficult coring andbrazing problems involved. Sheet metal fabrication has proven difficultdue to the requirement that the braze alloy melt at temperaturesconsiderably lower than the melting point of the parent material. Theselatter characteristics are particularly unsuitable for use in gasturbine engines operating at elevated temperatures.

The present invention provides solution to the fabrication problems ofthe prior art by permitting the installation of turbulence promotingnodes within slots and trailing edges (and similarly in other heatedplate applications) which result neither from casting nor sheet metalfabrications, by means of the formation of intersecting passages throughthe trailing edge by conventional means such as crossdrilling.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved cooling slot for use with heated plates.

It is a more particular object of the present invention to provide arelatively inexpensive and reliable cooling slot fabrication for use intrailing edge slots of airfoil blades.

It is another object of the present invention to provide a method forforming an improved cooling slot according to the present inventionwherein the limitations of sheet metal fabrication and casting areremoved from issue.

The foregoing, as well as other objects which will become apparenthereinafter, are accomplished in the present invention by the formationof a cooling slot by providing pluralities of intersecting passagesextending downstream of an internal blade cavity and through thetrailing edge. The intersections of the plurality of passages define anumber of nodes at points between the intersections. In one embodimentof the present invention, two pluralities of passages extend through thetrailing edge, each plurality aligned at a predetermined angle withrespect to the trailing edge, the passages of each plurality beingsubstantially parallel with one another, and the passages of bothpluralities being coplanar. The shape of the resulting nodes can bedetermined by the shaping of the passages as well as by the angle of thepassages with respect to the trailing edge and by the spacing of thepassages. It has been found that improved heat transfer efficiencyoccurs when the nodes are formed with a sharp point at their upstreamends within the slot.

The present invention also provides a method for the formation of theimproved cooling slots, the method, in one form, including the steps offorming a first plurality of cooling passages, and forming a secondplurality of cooling passages wherein preselected of the second passagesintersect preselected of the first passages defining a plurality ofnodes.

BRIEF DESCRIPTION OF THE DRAWING

The characteristics of the present invention will be described withparticularity in conjunction with the appended drawing wherein:

FIG. 1 is a cross-sectional view of an airfoil blade incorporatingelements of the present invention; FIG. 2 is a perspective view inpartial section of a trailing edge slot according to the presentinvention incorporated within the blade of FIG. 1; and

FIG. 3 is a section view of a trailing edge cooling slot similar to thatin FIG. 2, and taken along line 3--3 of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The cooling slot of the present invention will be described hereinafterin conjunction with and in the environment of an airfoil blade suitablefor use as a compressor blade or a turbine blade of a gas turbineengine. It will become apparent that the concepts of the presentinvention are not limited to such application, but are suitable for usein diverse applications wherein a heated plate is desirably cooled by afluid passing therethrough.

An airfoil blade 10 in partial section view is depicted in FIG. 1. Theblade has a leading edge 12 and a trailing edge 14 in addition to aninternal cavity 16 which, during operation, houses a quantity of coolingfluid. The body portion 18 of the blade is capped by a tip cover 20which isolates the internal cavity 16 from the environmental atmosphere.A trailing edge cooling slot 22 extends downstream from the cavity 16within the trailing edge 14 and provides communication between thecavity 16 and the trailing edge 14 and opens into the surroundingatmosphere downstream of the trailing edge.

FIGS. 2 and 3 combine to disclose pertinent characteristics of thepresent invention relating to the trailing edge cooling slots 22 ofblade 10. These Figures disclose that the trailing edge slot 22 isformed of a plurality of individual passages extending downstream frominternal cavity 16 and opening through a number of exit ports 24 intothe atmosphere downstream of the trailing edge 14. More particularly, inthe embodiments depicted in FIGS. 2 and 3 of the present invention, thetrailing edge slot is formed of a first plurality of passages 26substantially parallel with one another, coplanar, and aligned in apredetermined first angle θ₁ with respect to the trailing edge 14 of theblade 10. A second plurality of passages 28 cooperates therewith, thelatter plurality also being parallel, coplanar and aligned at an angleθ₂ with respect to the trailing edge of the blade. In this form, thepassages 26 and 28 may be formed by crossdrilling - that is, by drillingthe first set of passages at an angle of θ₁ opening through ports 24,and subsequently drilling the second plurality of passages at an angleof θ₂ opening through the same exit ports 24.

In this configuration, the first and second pluralities of passages areformed in such a way that preselected of the passages of one pluralityintersect at least one of the passages of the other plurality. In thepresent embodiment, substantially all individual passages intersect anumber of passages of the other plurality. As a result, a plurality ofnodes 30 is defined between the points of intersection of the twopluralities of passages 26 and 28. The shape and size of the nodes 30 isdetermined by the shape, size, position, and orientation of thepluralities of passages. Hence, an optimum node shape and size may beattained and effectuated easily by adjusting the aforementionedparameters. Suitably the nodes 30 depicted in FIGS. 2 and 3 aresubstantially rectangular in cross section.

The present invention also comprehends a method for forming theplurality of nodes 30 of trailing edge cooling slot 22, and this methodcomprises the steps of: forming the first plurality of passages 26extending from internal cavity 16 through trailing edge 14 at an angleθ₁ with respect to the trailing edge, the passages of the firstplurality being substantially parallel with one another and coplanar;forming the second plurality of passages 28 extending through thetrailing edge 22 at a predetermined second angle θ₂ with respect to thetrailing edge, the members of the second plurality being substantiallyparallel with one another and coplanar; and preselected of the secondplurality of passages aligned to intersect at least one of the firstplurality of passages to form a number of nodes between the points ofintersection thereof. As has been stated above, the present invention,and more particularly the method for forming a cooling slot, isadaptable to use with any heat plate wherein such cooling is suitablefor operation.

During operation of the associated gas turbine engine, a cooling fluidis delivered by means not shown into the internal cavity 16 of blade 10.A portion of this fluid is directed through cooling slot 22 of thetrailing edge 14 in order to cool the trailing edge. As this fluidpasses through the multiplicity of passages 26 and 28 forming coolingslot 22 and prior to its exit through ports 24, the fluid engages thenodes 30. The nodes serve to increase the surface area of the slotpresented to the fluid for heat transfer therebetween, as well as topromote turbulent fluid flow within the slot. Both of thesecharacteristics result in improved heat transfer, and an attendantreduction in cooling fluid expenditure. The method and configurationpresented by the present invention enable such a slot to be manufacturedand utilized without the unfortunate drawback cited with respect to theprior art.

While the present invention has been disclosed in a particularembodiment thereof, the concepts of this invention are not limited tosuch embodiment. For example, while the presentation herein is limitedto airfoil blades, similar constructions and techniques fulfill similarrequirements with respect to other types of heated plate structures.Also, while the method described herein involves drilling, otherhole-forming methods will suffice. Those skilled in the art will be ableto devise other variations without departing from the spirit of thepresent invention. It is contemplated that such variations beincorporated within the appended claims.

What is considered new and desired to be secured by Letters Patent ofthe
 1. A method for forming a plurality of polygonal nodes within atrailing edge slot of an airfoil blade, the blade having an internalcavity and a trailing edge, the method comprising the steps of:formingat least two sides of each of said polygonal nodes by forming a firstplurality of passages extending from said cavity through said trailingedge and aligned in a predetermined first angle other than substantiallynormal with respect to said trailing edge; and forming at least twoadditional sides of each of said polygonal nodes by forming apreselected second plurality of passages intersecting at least a portionof said plurality of passages and extending from said cavity throughsaid trailing edge and aligned in a predetermined second angle
 2. Themethod of claim 1 wherein:individuals of said first plurality ofpassages are formed substantially parallel with one another; andindividuals of said second plurality of passages are formedsubstantially
 3. The method of claim 2 wherein:
 4. The method as setforth in claim 1 wherein the steps comprising the forming of said firstand second plurality of passages include drilling of at least a portionof said first and second plurality of passages.